Highly selective keying circuit



March 19, 1957 D. M. WHERRY HIGHLY sELEcTlvE KEYING CIRCUIT' Filed Dec.10, 1955 HIGHLY SELECTIVE KEYING CIRCUIT Donald M. Wherry, Camarillo,Calif. Application December 10, 1953, Serial ANo. 397,496 12 Claims.(Cl. Z50-36) (Filed under Rule 47(0) and 3s U. s. C. 11s) The inventiondescribed herein may be manufactured and used by or for the Governmentof the UnitedStates of America for governmental purposes without thepayment of any royalties thereon or therefor.

The present invention relates to a highly selective keying circuit andmore particularly to a highly selective keying circuit utilizing anarrangement wherein the noise and ringing encountered in conventionalhighly selective circuits are substantially eliminated.

The invention circuit is especially adapted for use in code reception,and it may be employed as a selective auxiliary circuit for use inconjunction with a standard amateur receiver or the like. It isobviously desirable to utilize highly selective circuits in codereception operations, but as is Well-known in the art, such circuitscause ringing at both audio and radio frequencies which eventuallycauses the circuits to be unusable as the selectivity is increased.Furthermore, operator fatigue caused by the characteristic noiseassociated with the highly selective circuits also places a practicallimitation upon the amount of selectivity permissible in' code receptioncircuits.

VThe audio output signals of a conventional amateur receiver or the likeare fed into the invention circuit wherein a keyer means controls theoperation of a relaxation oscillator which provides the output signalsof the circuit. The keyer means is selectively biased such that thesignal it is desired to receive will trigger the oscillator, butsubstantially all noise and interfering signals of less magnitude thanthe desired signal will not trigger the oscillator, thereby greatlyreducing operator fatigue.

The output of the circuit may be adjusted to produce a tone pleasant tothe ear, and since the output of the circuit is produced only by therelaxation oscillator therein, no ringing will be present in the output.

An object of the present invention is the provision of a new and novelhighly selective keying circuit which substantially eliminates the noiseassociated with high--` ly selective circuits. j t

Another object is to provide a new and novel highly selective keyingcircuit whichlsubstantially eliminates all ringing A further object ofthe invention is the provision of a new and novel highly selectivekeying circuit which is simple and inexpensive in constructioinyetsensitive and' reliable in operation.

Other objects and many of the attendant advantages 'nited States PatentO of this invention will be readily appreciated as the saineA rice Fig.1 a cathode follower 10 which is adapted to receive the audio outputsignals of a conventional amateur re-` ceiver or the like, the output ofthe cathode follower being connected to the input of a highly selectiveaudio band pass filter 11. The output of the filteris connected to theinput of an amplifier 12, and the outputl of the `arnplier is connectedto the input of a rectifier 13 which changes the A. C. voltage output ofthe'amplilier` into a D. C. voltage. The D. C. output of the rectier isconnected to a keyer 14 which is connected to and controls the operationof a relaxation oscillator 15. A power supply 16 energizes the entirecircuit, and a-suitable means such as a pair of earphones 17 `isconnected to the output of the oscillator.

Y Referring now to Fig. 2, it may be seen that a first input terminal 20is connected to ground and a second input terminal 21 is connected tothe grid of a triode cathode follower tube 22, the plate of the tubebeing connected to the power supply and the cathode of the tube beingconnected to ground through a fixed resistor 23 and a variable resistor24. The cathode follower is suitably designed so as to provide theproper impedance match between the input of the invention circuit andthe ouput of the receiver to which the circuit is connected. A capacitor25 couples the output of tube 22 to the grid of a triode amplifier tube26, and capacitor 25, coil 27, resistors 23 and 24 comprise a resonantcircuit, the selectivity of which may be adjusted by means of variableresistor 24. Capacitor 25 and coil 27 are designed to provide a highlyselective audio band pass filter in accordance with the audio frequencywhich is normally fed into the input of the circuit.

The cathode of tube 26 is connected to ground through a` conventionalcathode bias resistor 28 and a by-pass capacitor 29, and the plate ofthe amplifier is connected to the power supply through a load resistor30. A capacitor 35 serves as a high frequency by-pass to .ground for theoutput of the amplifier and capacitor 36 couples the output of theamplifier to rectifier 13 which comprises two plate-grid connected tubes37, 38 which are disposed in a voltage doubling rectilier arrangement. l

Capacitor 40 and resistor 41 serve as a filter to remove the ripple fromthe output of rectitier 13, resistor 41 also serving to couple theoutput of the rectifier to the grid of a keyer tube 45. The grid of tube45 is also connected to the cathode of tube 37 through a bias resistornetwork including iixed resistors 46, 47 and a selectively variableresistor 48.

Resistor 50 limits the plate current of tube 45 to a desired value andcouples the output of the keyer tube to a relaxation oscillatorcomprising a neon bulb 51, a selectively variable resistor 52 connectedin series therewith to ground, and a capacitor 53 connected'in paralleltherewith. A xed resistor 54, and a selectively variable resistor 55connect the oscillator to the power supply. Resistor 52 is adapted tovary the magnitudeor volume of the output signal of the oscillator,V andresistor 55 is adapted to vary the frequency or tone of the outputsignal of the oscillator.,

With no signal input and-no bias present on tube 45, the plate currentdrawn by the tube causes'such a large voltage drop in resistors 54 and55 that tube 51 will not ionize and consequently there will be no outputsignal' developed by -the oscillator. When an input signal is impressedon the circuit, a negative D. C. voltage is applied to the grid of tube45 which cuts olf the tube, thereby interrupting the flow of platecurrent and allowing the voltage on tube 51 to build up and 'cause asawtooth oscillatory output `voltage to be developed bythe oscillator.

A first switch terminal 60: is conneteclfbetween'an electrode of 'tube51 and resistor 52, and asecbnd switch arcanes terminal 61 is connectedto input terminal 21. A singlepole double-throw switch 62 is adapted tobe selectively actuated to engage either contact 60 or 6i, and theswitch is connected to a first output terminal 63. A second outputterminal-64 is connected'to ground, and'itjis evi,- dent-that'wherrswitch 62 is in the position shown, the output is taken across theinvention circuit, but thatfif it isdesired to ,doV so, the switch may`be actuated to, engage contact- 61\ and by-passthe circuit, taking theoutput across the input't'erminals 2t) and 21.V4 i

The-power supply 16 includes two terminals 65 and 66which'areadaptedtube-connected toa suitable A. C..

voltage'f'sourc'e, and-aswitch 61 is adaptedrto energize or`deenergizeithecircuiti*-CoilfS represents the primary windingl'ofatrns`foimer Vand coils 69-and 70 respectively Irepresentthesecondary/and filament lwindings of cluding means for damping saidresonant circuit for filtering -said signals, means for amplifying saidfiltered signals, means for rectifying said amplified signals, keyermeans energized by said rectified signals, oscillator means controlledby said keyer means, and a source of power for each of saidaforementioned means.

2. A circuit as defined in claim l including a variable resistor networkadapted to biassaid keyer means whereby the threshold value of saidkeyer means may be varied.

3. A highly selective keying circuit which comprises Van impedancematching means, a low frequency resonant circuit including means fordamping said resonant circuit,

the transformer. The' filament winding provides the power for the heaterfilaments (not shown) of eachv ofthe tubes' in the" circuit.'- -Thelower end ofcoil 69 is? connected to ground and the upper end thereof isconnected to a diode rectifier71 which may be a selenium rectifier orthelike whereby theA; C.-'voltage induced in secondary windingi69 ischanged into `a D. C. 4voltage for energizing the circuit. lCoil Y72 andcapacitors73, 74 provide a filter for reducing the ripple ofthe powersupply voltage;

In Voperation, the crcuit'is initially adjusted suclithat filter 11exhibits a`highly'sel'ective band pass characteristic to the-audi-oinputsignal impressed on terminals and 21; `and tube'26 is designed formaximum gain., It isV Y apparent .that a'positive biasing voltageisimpressed on the grid of tube 45 through the resistor network includingresistors 46'48 and that byselectively varying the resistancef oflresistorv48, the 'positive bias Von the tube maybe altered. The positivebias on the grid of tube 45' is adjust'edsuch that it is slightly less,e. g. Yone-quarter volt, than the negative voltage impressed thereon byvthev signal fwhicli it is desired to receive whereby the signal will`cut off the tube and key tlieoscillator.A f ln this mannen-,the desiredsignal actuates oscillator 15, yet Vany noise or interfering signalsproducing a potential on the keyer grid less than that of the positivebias thereon will not ti'igger theosci'llator. 1 it is thereforeapparent thatby properly adjusting the threshold value of tube 45 bymeans of resistor 48,'.the keying voltageY level can'be set above thatvof .any interfering signal, even in the case Where the interferingsignal is on the same frequency as the desired signal. Y It should benoted that by utilizing the invention circuit, it would also `bepossible to transmit and receive code and telephonesignals-simultaneously on the same radio frequency channels andthatmultiple code channels on one frequency would be greatly simplified.

Although a. preferredeinbodiment of the present invention has beenl-sliowniand described, it is apparent thatkv other well-knownelectronic tubes and components may be substituted for those employed ineach of units 10a-16. Forexample, ahigh gain pentode Vmay beYsubstituted for` .tub'eZ 'and two crystal diodes couldy be used inplace. of

tubes 37`and- 38, A 'sharp cutoff Vpentode could be used as thekeyertube, and various other well-known relaxation l oscillatorsrco'uldreplace VtheV one shown in the drawings.

I IFrornlthe foregoing, it is evident that thereis provided Ya new andnovel highly selective keying circuit which substantially eliminates thenoiser and ringing associated with-'highly selective circuits; andwhichV is simple and inexpensive-in construction, yet sensitive andreliable in operation.'` 1 .y 'Y ','Obviouslymany modifications 1andvariations of the .said impedance Vmatching' means, an amplifierconnected to the outputof said resonant circuit, a rectifier'connectedto the output of said amplifier, a keyer connected to the output of saidrectifier, an oscillator connected to the output of said keyer, and asource of powertor said plifier means connected :to said resonantcircuit, rectifier means connected to said amplifier means, keyer meansconnected to said rectifier means, a variable resistor network connectedbetween said rectifier' means fand said keyer means whereby thethreshold value of said keyer means may be varied, relaxation oscillatormeans con nected to said keyer means, and a source'of power for saidcircuit.

5. A circuit as defined in claim 4 including means for adjusting theselectivity of said ,resonant circuit.

6,. Alcircuit as defined in claim 4 including means for adjusting thefrequency of said oscillator means.

7. A circuitas defined in claim 4 including means for filtering theoutput'of said rectifier means.

8. A lhighly selective keying circuit which comprises a signal'input-means connected to a cathode follower means, a low frequencyresonant circuit including means for damping said resonant circuit, saidresonant circuit being connected to the output of said Vcathode followermeans, an amplifier means connected `to the output of said'resonantcircuit, rectifier means connected to thc output of'said amplifiermeans, filter means connected` to the output of said rectifier means,keyer means connected to-the output of said second filter means, aresistorr network connected between lsaid rectifier means and saidkeyermeans,',at least one resistor in said re.

sistor4 network being selectively variable, oscillator means connectedto the output of said keyer means and' controlled thereby, output meansconnected to the output connected to the output of said oscillator meansor dipresent invention `are possible in the light of the above Yteachings. VIt istherefo're Yto be Yunderstood that within the scope ofthe appended claims the invention'may'b'e practiced otherwise lthanasspecifically described.

V"Iclaimi l. A highly selective keyingcircuit which coiripris'esIVV asource of signals, alowIfreqi'iefncy' resonant circuit iiirectly to saidinput means.

an input means connected to the grid of a cathode fol# lowerAtube,'thegoutp'ut of said 'cathode follower being i connected to a lowvfrequency resonant circuit including means Yfor damping said resonantcircuit, means for adjustingthe selectivity ofsaid resonant circuit, theoutput of, said resonant 'circuit 'being connected to the grid of anamplifier'itube, the outputiofsaid amplifier tube being connectedtoa-rectifier means comprising a plurality of plate-grid'connected.tubesdisposedin a voltagel doubling arrangemennjme Voutput of said rectifierlmeausjueing couple-'d'by a'filter means to' the grid of 'akeyeij tube.a tor network connected between said rectifier means Me'gridfofsaidkeyer tube, .atleast oneresistorin network Vbeing",variable,iaA relaxation ,oscil- References Cited in the file of this patentUNITED STATES PATENTS Overacker July 26, 1932 Hagen May 23, 1933 ProtzeFeb. 8, 1938 Spencer et al. Ian. 3, 1939 Bliss Jan. 31, 1950

